jme: Remove shadow register support

The hardware failed to update the shadow register in several cases.
It's known to be failed at 64bit box with more than 4G RAM.
In order to make the device working stable, give up using the shadow
register feature.

Signed-off-by: Guo-Fu Tseng <cooldavid@cooldavid.org>
Signed-off-by: David S. Miller <davem@davemloft.net>